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Tuesday, June 5, 2012

The ShakerBOT: Snakeboard inspired robot

When one thinks about robot locomotion, the first thing that comes to mind are bipedal robots or mobile wheeled robots. This is not the case with Sevag Babikian. As part of a research done by the Mechanical Engineering department at the American University of Beirut, Sevag built a wheeled robot which motion is inspired from the snakeboard. He called it the ShakerBot.

What is the ShakerBot made of?

As we can see above, the Shakerbot is made up of the following components:

- A plexiglass laser cut chassis

- A central DC motor connected to a 2kg metallic flywheel

- A couple of DC motors (steering motors) on the front and back. These motors are called steering motors and they are connected to an axle which in turn is connected to friction wheels to guide the robot.

- A couple of castor wheels on both sides of the robot to support its weight.

All the motors are connected to quadrature encoders to compute their instantaneous position and speed. Each motor is driven using an L298 based motor driver circuit, capable of driving up to 4A continuously.The brain of the Shakerbot is an Arduino Mega board. The Arduino Mega communicates wirelessly via bluetooth (ARF32 module) to a PC for teleoperation.

So, how is motion generated on this ShakerBot?

Have you ever seen a snakeboard? Or have you ever felt the urge to kneel on a rotating chair and start turning in order to experience the effects of inertia, or those of dizziness? Well, ShakerBot operates on the same principle. The flywheel generates momentum which drives the robot around. Steering motors, as well as the flywheel, move in a sinusoidal fashion. The motion pattern of the flywheel and of the steering motors are what generate the different robot motions (forward, backward, rotation, parallel park etc.). The mathematics are quite complicated and can be fully understood in this publication by Lewis A. et al (1993).

The following video explains the mechanism better

The Arduino Mega board does all the complex mathematical and trigonometric equating and controls the DC motors accordingly.

How does the ShakerBot communicate with the PC?

As mentioned above, the computing is done on the Arduino Mega board. However, it is required to have a wireless connection with a PC in order to teleoperate the ShakerBOT and tell it where to go. A couple of months ago I received a bluetooth module from Farnell electronics. It is the low cost ARF7044A based on the ARF32 bluetooth module manufactured by Adeunis (you can find it on the Farnell Electronics website). I decided to help Sevag out in implementing the bluetooth communication on the ShakerBot using this board. For 23£ I can tell you that this chip worked like a charm. We were able to achieve instantaneously a wireless communication, simply by wiring it to the serial Tx and Rx of the Arduino Mega and by connecting it to our laptop's bluetooth.

The ARF7044 connected to the arduino shield

I will be using more of this ARF7044 in the future and I will post whatever I find.

On another note, for all the electronics makers, geeks and hackers out there, I discovered lately a website with a large community powered by Farnell electronics that you should check out. It is called element14.

Sevag and his ShakerBOT

Concluding thoughts

The easiest mechanism for robot locomotion is the differential drive mechanism. However if we look at humans we see that we use bipedalism very efficiently. We can walk, run and even climb with minimal energy consumption. This is because we make use of gravity to ease up the locomotion. Up until now, every attempt to mimic human bipedalism on humanoid robot has been very inefficient. This might change as technology as we learn how to fully harbor the physics and dynamics of the system. Same thing can be thought about this ShakerBOT. Humans use snakeboard efficiently, they harbor the momentum generated by their bodies in order to propel. Maybe this ShakerBOT and after plenty of modifications and improvements will turn out to be an efficient locomotion method after all.

Finally, I am very excited to see the maker movement growing fast in Lebanon. First Mounir and his Octocopter and now Sevag and his ShakerBOT. I can ensure you that there many more creative people just waiting to expose their work!